A piezoelectric/electrostrictive actuator has an advantage that displacement can precisely be controlled in the order of submicrons. Especially, in the piezoelectric/electrostrictive actuator in which a sintered body of a piezoelectric/electrostrictive porcelain composition is used as a piezoelectric/electrostrictive body, in addition to the advantage that the displacement can precisely be controlled, there are other advantages that the actuator has high electromechanical change efficiency, large generative force, high responsivity, high durability and small power consumption, and the actuator using these advantages is employed in a head of an ink jet printer, an injector of a diesel engine or the like.
As the piezoelectric/electrostrictive porcelain composition for the piezoelectric/electrostrictive actuator, heretofore, a Pb(Zr, Ti)O3(PZT) based piezoelectric/electrostrictive porcelain composition has been used, but there has been a strong fear of an influence of solute of lead from the sintered body on global environments, and hence an (Li, Na, K) (Nb, Ta)O3 based piezoelectric/electrostrictive porcelain composition has been investigated.
An (Li, Na, K) (Nb, Ta)O3 based piezoelectric material is usually sintered in the air or an oxygen atmosphere at 1020 to 1250° C. for 0.15 to 4 hours (e.g., Non-Patent Documents 1 to 3). A heating rate to reach a firing temperature is 200° C./h or 300° C./h, and the temperature rises at a constant heating rate from room temperature to the firing temperature (e.g., Patent Document 1).
There is also a research example in which the temperature is kept in a range of 600 to 650° C. for 1 to 5 hours in the heating process, whereby an organic binder added to improve formability of powder is removed (a de-binder process) (e.g., Patent Document 1). Microstructure of the sintered body includes grains of around 10 μm (e.g., Non-Patent Document 1). Moreover, there is a study example aimed at orientation structure of the sintered body (e.g., Non-Patent Document 4).    [Non-Patent Document 1] M. Matsubara et al., Japanese Journal of Applied Physics 44 (2005) pp. 6136-6142.    [Non-Patent Document 2] E. Hollenstein et al., Applied Physics Letters 87 (2005) 182905    [Non-Patent Document 3] Y. Guo et al., Applied Physics Letters 85 (2004) 4121    [Patent Document 1] JP-A-2006-028001    [Non-Patent Document 4] Y. Saito et al., Nature 432, 84-87 (2004)
Conventionally, study has been conducted aiming at a microstructure or orientation structure having small and uniform grain diameter for the purpose of improving electrical properties. However, for example, electric-field-induced strain S4000 is insufficient at 400 to 550 ppm, and it is desired to develop a piezoelectric material which is higher in electrical properties such as electric-field-induced strain.